I'm a big fan of carrying a pocketknife and tend to use my Swiss Army Knife at least once per day. Unless you're a frequent wine drinker the corkscrew doesn't have too many other uses, but it does work well to help loosen up knots in various types of string or cord.

Bushcrafting weblog Rocky Mountain Bushcraft shares that if you insert the point of a corkscrew into a jumbled knot you can use the pointed tip to help loosen the knot much better than using your fingers. Of course you don't need to specifically have a Swiss Army Knife—any corkscrew will do.